A thermoelectric conversion material that allows mutual conversion between heat energy and electric energy is used for a thermoelectric conversion element such as a thermoelectric generation device and a Peltier device. In thermoelectric generation to which the thermoelectric conversion material or the thermoelectric conversion element applys, heat energy can be directly converted into electric power, and a movable part is not required. Thus, the thermoelectric generation is used for a wrist watch operated by body temperature, a power supply for remote districts, a space power supply or the like.
As one indication for evaluating the thermoelectric conversion performance of the thermoelectric conversion element, there is a dimensionless figure of merit ZT (hereinafter, simply referred to as a figure of merit ZT in some cases). This figure of merit ZT is represented by the following Equation (A), and for enhancement of the thermoelectric conversion performance, it is required to increase a thermopower per absolute temperature of 1 K (hereinafter, referred to as a thermopower in some cases) S and an electrical conductivity σ, and to decrease a thermal conductivity κ.Figure of merit ZT=S2σT/κ  (A)
In Equation (A), S(V/K): thermopower per absolute temperature of 1 K (Seebeck coefficient)
σ (S/m): Electrical conductivity
κ (W/mK): Thermal conductivity
T(K): Absolute temperature
Preferable thermoelectric conversion performance is required for the thermoelectric conversion material, and thus a material which is mainly put into practical use at the present day is an inorganic material. However, the inorganic material needs a complicated processing process for using in the thermoelectric conversion element, is expensive, and contains harmful substances in some cases.
On the other hand, an organic thermoelectric conversion element can be produced at a relatively low price and facilitated to process for forming a film or the like. For these reasons, recently, researches have actively been carried out, and eventually an organic thermoelectric conversion material and a thermoelectric conversion element using the same have been reported. In order to increase the figure of merit ZT for thermoelectric conversion, an organic material having high Seebeck coefficient and electrical conductivity and low thermal conductivity is demanded. For example, a thermoelectric conversion element, which includes a carrier transportation layer formed by an organic semiconductor material such as pentacene and a carrier generation layer of tetrafluorotetracyanoquinodimethane or the like, is proposed (see Patent Literature 1). In addition, a conductive polymer or a charge-transfer complex is proposed as an organic compound in a thermoelectric material including an organic compound and a dopant (see Patent Literature 2). Moreover, phthalocyanine is proposed as a thermoelectric conversion material (see Patent Literature 3). A metal phthalocyanine is proposed as a p-type semiconductor material to be used in a thermoelectric conversion element (see Patent Literature 4).